Understanding the Cargo Hold Coating Challenge.
Cargo hold coatings play a critical role in protecting the revenue-generating areas of bulk carriers, but they are exposed to some of the most aggressive environments found onboard a vessel. Safinah’s webinar, “Cargo Hold Coatings Exposed: What Can Go Wrong? Why It Happens”, draws on the company’s practical experience in coating application, inspection and failure investigation to examine why cargo hold coatings deteriorate, the factors that influence their performance, and how owners and operators can reduce the risk of premature failure.
Safinah’s failure investigation experience demonstrates the commercial relevance of the issue. Around 12% of the coating failures investigated by Safinah relate to cargo hold coatings. Although this is lower than underwater hull and cargo tank coating cases, cargo holds coating deterioration can create significant operational and financial consequences.
The foundations of effective coating performance.
A central message of the webinar is that cargo hold coating performance depends on more than the coating product itself. For a system to perform as expected and specified, the steel or existing substrate, including a coated surface must be correctly prepared; the coating must be appropriate for the anticipated operating conditions and cargoes; and application and curing must follow the paint manufacturer’s technical requirements. Failure in any of these areas significantly increases the likelihood of premature breakdown.
Choosing the right cargo hold coating.
Cargo hold coatings are generally epoxy-based and range from basic modified epoxies to upgraded pure epoxies and further to premium abrasion-resistant systems specifically formulated and tested for use in cargo holds. The webinar highlights an important lifecycle consideration: while premium products require greater initial investment and more demanding surface preparation, they can substantially extend intervals between major refurbishments.
Basic systems such as modified type epoxies may require major refurbishment at approximately five years, compared with around seven to ten years for pure epoxies and approximately 12.5 years for premium systems. Higher-performing products, however, typically demand higher standards of abrasive blasting and steel profile preparation to deliver their intended long-term performance.
An exceptionally aggressive operating environment.
The need for robust performance reflects the severity of the cargo hold environment. Cargo hold coatings can simultaneously face impact, abrasion and gouging from cargoes and loading equipment; chemically active cargoes including coal, bauxite, sulphur and petcoke; high temperatures and humidity; seawater exposure; salts; oxygen; and potentially aggressive acidic conditions.
Consequently, coatings may experience staining, scratching, corrosion, blistering, cracking, delamination, adhesion loss and softness. Mechanical damage can also expose the underlying steel, creating conditions where corrosion can develop and accelerate.
Why Cargo Hold Coatings fail.
Safinah’s investigations show that failures can mainly originate from poor shipyard workmanship and subsequent commercial operations. Shipyard-related problems include excessive dry film thickness, solvent retention caused by restricted ventilation, incorrect overcoating intervals, poorly adhered cosmetic coatings, grit contamination, inappropriate coating selection and inadequate preparation of existing systems.
Operational causes include loading hard angular cargoes too aggressively, insufficient curing before first cargo, inadequate temporary protection when carrying sulphur, poorly prepared onboard repairs, high-speed cargo distribution and mechanical damage from grabs, excavators and other equipment.
Lessons from real-world failure investigations.
The webinar’s case studies demonstrate why identifying the true root cause is essential so future mistakes are minimised. One case traced widespread delamination back to inadequate steel profile (low) and extreme coating over-application at newbuilding, with approximately 1,200 microns applied where around 200–250 microns would typically have been sufficient. A later maintenance coating added further stresses when curing, exposing adhesion weaknesses in the original system resulting in total scheme detachment.
Another investigation concerned a failure initially attributed to cargo exposure. Safinah found instead that inadequate surface preparation had left corrosion and scale beneath the newly applied coating. The case also highlighted the risk of loosely defined requirements such as “sweep blasting”, which can be interpreted differently between shipyards and may leave corrosion behind.
Sulphur carriage provides another important lesson. Temporary protective systems such as lime wash or other specialist water-based low volume solid coatings can protect exposed steel, but only when applied correctly and at sufficient thickness. In one case, approximately 20 microns of uneven lime wash was applied before a 72-day sulphur voyage, resulting in significant corrosion and pitting of the uncoated tank top.
Extending coating life and reducing repair costs.
Ultimately, no cargo hold coating can eliminate every form of mechanical damage or resulting corrosion. However, selecting a system formulated for the intended cargoes, preparing the substrate correctly and controlling application and cure can significantly delay deterioration, reduce the risk of cargo hold rejection and extend the interval between costly major repairs.
Test Patching: Building an evidence-based coating strategy.
The webinar concludes by advocating cargo hold test patching as a practical way to evaluate higher-performance systems before committing to a full-scale upgrade. Owners can trial alternative products alongside their existing coating system and independently assess comparative performance under actual operating conditions.
By monitoring test patches, controlling application quality and interpreting results against the vessel’s cargo profile, owners can determine whether the additional investment in premium coatings delivers measurable benefits through reduced maintenance, longer refurbishment intervals or greater flexibility in the cargoes carried. This shifts coating selection away from upfront price alone towards a more informed lifecycle cost, risk and long-term asset performance strategy.
Q&A
What's the biggest contributor to the failure in service of a Cargo Hold coating.
Based on the failures we have been asked to investigate, the two biggest contributors are surface preparation and application conditions.
Coating manufacturers thoroughly test their products to ensure they are suitable for their intended use. However, these products are tested under defined conditions and specified surface preparation standards – whether that involves a full Sa 2 blast, water jetting, spot blasting, or another specified method.
The challenge arises when the conditions during application in the dry dock do not meet those requirements. When we investigate coating failures, we often find issues such as:
- An inadequate surface profile remaining from the newbuild stage
- New coatings being applied over poorly prepared existing surfaces
- Poorly controlled spot blasting
- Contamination remaining on the substrate
- Loose coating or lifting edges not being properly prepared
- Moisture, condensation or even ice remaining on surfaces during application
Our advice is to treat cargo holds as a critical, revenue-generating area of the vessel. They may not always require the same level of control as cargo tanks, but the quality of the coating work can have a significant impact on operational performance and maintenance requirements.
Before coating is selected, the surface preparation requirements should be understood, and also, there must be assurances from the shipyard that they can meet those requirements within the agreed budget.
Surface preparation should be carried out in accordance with the coating manufacturer’s technical data sheet, and the selected coating must be appropriate for the intended service conditions.
It is equally important to assess any existing coating that will remain in place, after spot blasting for example. Adhesion checks should be carried out to confirm that the existing coating remains sound and well adhered to the steel substrate, particularly on areas such as the undersides of cross-decks. Environmental conditions should also be carefully controlled to ensure surfaces are free from moisture, condensation or ice before overcoating.
Ultimately, one of the most effective ways to reduce the risk of coating failure is to have the work independently supervised and managed. An independent project manager working on behalf of the owner can verify that surface preparation, application and quality control meet the agreed specification and help ensure that the shipowner receives the standard of work they expect.
When applying an abrasion-resistant coating that requires a specific surface profile, it is sometimes suggested that hydroblasting can “reveal” the original newbuild profile. Is this actually the case?
There is nothing inherently wrong with water jetting as a surface preparation method, and it offers several advantages. However, it is important to understand that water jetting cleans the existing surface but does not create a new surface profile.
If the original steel profile is inadequate, water jetting will essentially leave that profile unchanged. The surface may look very clean after water jetting, but the underlying profile may still be insufficient for the coating being applied.
This becomes particularly important when investing in a premium abrasion-resistant coating system that requires a specific surface profile (depth) to achieve its intended performance. Before drydocking, owners should therefore understand the condition and profile of the existing steel and determine whether the proposed surface preparation method will meet the coating manufacturer’s requirements.
How can we minimise the risk of damage from the end of application to loading the first hard cargo?
Coating cure time is an important consideration, particularly when trying to prevent early damage such as gouging.
Coating manufacturers provide application guidelines and technical documentation specifying the required time to first loading. This is the period needed for the coating to cure sufficiently before a particular cargo can safely be loaded.
The required curing period can vary depending on the cargo. A softer cargo may be less demanding on a newly applied coating, while harder or more abrasive cargoes may require the coating to achieve a greater degree of cure before loading.
Most importantly, curing time is highly dependent on temperature.
For example, a coating may require six days before first loading at a steel temperature of 15°C. However, if temperatures fall significantly overnight – perhaps to 5°C – the coating will cure more slowly. Simply calculating six days based on the daytime temperature may therefore underestimate the actual curing period required.
At lower temperatures, the time required before first loading can increase significantly, potentially doubling or even tripling compared with warmer conditions.
Ensure the cargo hold remains open after application, with adequate ventilation to ensure solvent evaporation.
To minimise the risk of early coating damage, owners and operators should consider the actual temperatures experienced throughout the entire curing period, not just daytime conditions. Where operationally possible, it may also be beneficial to:
- Load softer cargoes first
- Avoid dropping hard or angular cargoes from significant heights
- Reduce high-speed loading during the coating’s early service period
- Allow additional curing time whenever conditions permit
The key is to protect the coating during its critical early stages. After investing in surface preparation and a high-performance coating system, allowing sufficient curing time under the correct conditions is essential to achieving the expected long-term performance.
In your experience, how does the long-term performance of cargo hold coatings prepared by water jetting and cherry pickers compare with traditional blasting and staging? Are there specific risks to coating durability, and are today’s coating systems designed to accommodate this shift in surface preparation methods?
Water jetting can be an effective method of preparing cargo hold surfaces. It removes old or deteriorated coatings, rust and other surface contamination, leaving the steel clean and ready for further treatment. However, there are several important considerations that can affect long-term coating performance.
The key limitation is that water jetting does not create a new steel surface profile. Only abrasive blasting can establish or modify the profile. Water jetting will expose the existing profile, so if that profile was inadequate to begin with, it will remain inadequate after preparation.
There are also two other important factors to manage: flash rusting and surface moisture. Flash rust should be kept within the limits specified by the coating manufacturer, and the surface should be sufficiently dry before coating application.
Some cargo hold coatings are formulated with a degree of surface tolerance and may accommodate slightly damp conditions. However, coatings should not be applied to wet or icy surfaces. This becomes particularly important with premium, high-performance coating systems, which typically have lower tolerance for compromised surface conditions and may require a properly abrasive-blasted surface to achieve their intended performance.
Overall, water jetting can provide effective surface preparation, but the process needs to be carefully controlled. The existing surface profile, level of flash rust and surface moisture should all be assessed before coating application to ensure the system has the best opportunity to deliver its expected durability and performance.
What can Safinah do to help the client get a good cargo hold job in terms of long in-service performance.
We’ve been involved in many cargo coating projects, from failure investigations when things have gone wrong to the more proactive approach of managing the coatings works in drydock projects where our role is to help ensure coatings are applied correctly.
One of the most important lessons from that experience is to get independent expertise involved as early as possible. If you want independent oversight during the drydock, there is significant value in bringing that expertise into the project beforehand especially at the planning stage.
The first step is making sure the right coating system is selected for the intended service. Is the product suitable for the cargoes the vessel will carry? Does it have a proven performance record under those operating conditions?
Through our involvement in drydock projects, we have built an extensive database of coating performance, including both underwater hull and cargo hold applications. This gives us practical insight into how different coating systems perform in real operating environments and helps inform product selection.
The next step is ensuring the specification, surface preparation and application requirements are appropriate. Coating manufacturers can provide valuable technical guidance on their products, while Safinah’s role is to provide independent advice on behalf of the shipowner – helping assess the available options and determine what is most appropriate for the vessel and its operational requirements.
By combining the right product selection with an appropriate specification and independent oversight during application, owners can maximise coating performance and reduce the risk of premature failure.
Ultimately, the objective is simple: get the coating strategy right from the beginning, apply it correctly and avoid an unnecessary return to drydock for costly reblasting and reapplication.
From your experience, how should the surrounding areas of the spot-blasted areas be prepared to achieve enhanced durability of the coating? Have you faced typical problems in those areas?
Spot blasting in cargo holds should be approached in much the same way as spot blasting elsewhere on a vessel. One of the main priorities is to avoid leaving loose or flaky coating edges around the blasted areas, as these can become weak points when the new coating is applied.
Good edge preparation is therefore essential. This can be challenging in cargo holds, particularly where access is limited to cherry pickers rather than full staging or scaffolding, but the objective remains the same: prepare the spot-blasted areas to a high standard and minimise poorly adhered edges around the repair area.
Where practical, it can also be beneficial to square up the repair areas rather than leaving numerous small, irregular patches. This approach is commonly used on hulls and can provide a more controlled surface for coating application. It may require additional blasting and therefore additional cost, but it can contribute to a more robust and durable repair.
Equally important is the condition of the existing coating that will remain in place. Before overcoating, it is essential to confirm that this coating is still sound, well adhered and has sufficient integrity to support the new system.
Applying a new coating over poorly adhered existing material creates an inherent weakness. As the new coating cures, the stresses generated can pull the underlying coating away from the steel. The result can be failure of both the original coating and the newly applied system.
For this reason, checking the adhesion and integrity of the existing coating before overcoating is critical, particularly in harder-to-access areas such as the undersides of cross-decks.
These upper areas can also experience higher steel temperatures during service as the deck heats up, introducing additional thermal stresses into the coating system. Ensuring that any coating left in place is firmly adhered to the steel is therefore an important part of reducing the risk of future failure.
Ultimately, effective spot repair is not simply about preparing the visibly damaged areas. It is also about ensuring that the coating surrounding those repairs provides a sound and stable foundation for the new system.
How often have you seen insufficient surface profile as a root cause of coating failure, meaning the original surface preparation was already inadequate at the initial coating stage?
In adequate surface profile has been a factor in more than one occasion over the past 12 months and is a recurring issue from previous years failure investigations.
Overall, we would say that roughly 60% of the failures we have investigated are as a result of poor or inadequate surface preparation either from newbuilding, or from a dry docking where the surface has not been prepared to the correct standard.
Are coating failures due to improper cleaning or conditioning with a subsequent incompatibility between previous and current cargoes common?
Coating failures related to poor surface preparation and cleaning before application are relatively common in cargo hold repair projects.
When a vessel enters drydock for cargo hold coating repairs, the quality of surface preparation is critical. If the required standard is not achieved, there is a much greater risk of premature coating failure. Typical issues we see include:
- Inadequate cleaning or contamination remaining on the surface
- Insufficient or incorrect surface profile
- Poorly feathered edges around spot-blasted areas
- Loose or poorly adhered existing coatings being left in place
- Excessive moisture remaining after water jetting
Moisture is particularly important when water jetting is used. The surface must be allowed to dry sufficiently before the new coating is applied. Applying a coating over a wet surface can lead to significant adhesion problems and subsequent coating failure.
If the question relates instead to cleaning cargo holds between different cargoes, that presents a different challenge. For example, moving from a coal cargo to a grain cargo may require a much higher standard of hold cleaning to ensure the space is suitable for the next cargo.
Different cargoes have specific cleanliness requirements, and transitioning between very different cargo types – such as coal and grain – can require extensive cleaning. In these situations, achieving the appropriate cargo hold cleanliness standard is essential to prevent contamination and ensure the vessel is ready for its next cargo.
Do you think owners pay enough attention to the conditions during the application of the cargo hold?
The answer is probably no. When we look at cargo tank coatings for chemical tanks, the industry generally recognises how sensitive these systems are to application conditions and, as a result, there is typically a high level of control throughout the process.
Surface preparation in cargo tanks is particularly rigorous. The steel may require preparation approaching Sa 3, with processes involving washing, abrasive blasting, further cleaning and, where required, additional blasting. Temperature, humidity and other environmental conditions also need to be carefully monitored, while dry film thickness (DFT) must be closely controlled throughout the application.
A great deal of attention therefore goes into ensuring cargo tank coatings are applied correctly.
With cargo holds, however, the same level of attention may not always be applied. Because cargo holds are large, relatively open spaces, there can sometimes be a perception that coating application is less sensitive or requires less control.
However, the fundamental principles remain the same for any coating system. If the surface is not properly prepared, there is a greater risk of failure. Similarly, if the coating selected is not suitable for its intended service, its performance can be compromised.
Cargo hold coating projects therefore deserve careful planning and control, particularly around surface preparation and application conditions. This includes ensuring that:
- Surfaces are prepared to the required standard
- Moisture is not trapped or left in upper and difficult-to-access areas
- Spot-blasted areas are properly prepared and feathered
- Loose or poorly adhered existing coating is removed
- Environmental conditions are appropriate for application
- The selected coating is suitable for the intended cargoes and operating conditions
This is also where independent oversight can add significant value. Safinah can represent the shipowner during the coating project, independently verifying that surface preparation, environmental conditions and application practices meet the agreed specification.
Ultimately, cargo holds may be very different environments from cargo tanks, but the principle is the same: good coating performance starts with the right product, the right surface preparation and controlled application.
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